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(11) | EP 1 484 659 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Variable output-type current source circuit |
| (57) Disclosed is a variable output-type current source circuit capable of varying its
output current in a stepwise manner without the complication in circuit configuration
and the increase in size of a semiconductor circuit board for incorporating the circuit
therein. The constant current source circuit comprises a first self-biasing type constant
current circuit (3a) configured such that first and second transistors (M1,M2) are
operable to cooperatively supply a given voltage across a resistor (RS) to generate
a stabilized current (IR1). In order to vary the output current, the constant current source circuit includes
a switching circuit (transistor M5) connected in series to a series circuit connecting
in series the first transistor (M1) and the resistor (RS), and a second constant current
circuit (4) connected in parallel to a series circuit connecting in series the first
transistor (M1), the resistor (RS ) and the switching transistor (M5). The second
constant current circuit (4) is also configured to serve as an activation circuit
for the first constant current circuit (3a). |